This invention relates to the protection of aircraft against missile threats, and, more particularly, to a method and apparatus for locating, identifying, and taking action against hostile targets such as missiles.
Missiles fired at aircraft are usually guided either by a light seeker or by radar. Of the various types of seekers, infrared light seekers pose some of the greatest problems to aircraft defense. Unlike radar seekers, infrared seekers are passive and do not emit a detectable signal prior to the firing of the missile. Pilots therefore have little warning of their presence prior to the firing of the missile. Infrared-guided missile systems are relatively inexpensive, and human-portable units are widely available.
There has been a continuing effort to develop sensor systems and countermeasures that are carried on aircraft and are used to detect missile threats, particularly infrared-guided missiles, and take action against the missile threats. The sensor system must be effective to detect the infrared signature of a relatively small-sized missile at as great a distance as possible, in order to allow time for the countermeasure to be effective. In one approach, a wide-angle, two-color staring sensor system has been suggested to be particularly effective in detecting threats. This approach is limited by its low resolution and thence its ability to detect potential targets at great distances and susceptibility to smearing of the image, as well as the incomplete status of the detector technology. Additionally, the detection and warning components of the system must be integrated with the countermeasures components of the system.
There is an ongoing need for an improved approach to the protection of aircraft against missile threats and the like. The present invention fulfills this need, and further provides related advantages.
The present invention provides a method and apparatus for the self-protection of aircraft against missile threats. The approach integrates a search, detection, and identification unit, combined with a directional countermeasure device. Searching is accomplished with high resolution over a large angular range to identify potential targets. Upon finding a potential target, narrow-angle viewing is performed to-determine whether the potential target is hostile. If the target is hostile, the directional countermeasure device, which is pointing at the hostile target by virtue of its being mounted on the gimbal of the searching apparatus, is utilized against the hostile target. The entire apparatus fits within a small form factor, and is fully automatic in its operation.
An aircraft self-protection system comprises a gimbal platform, and a gimbal-platform servo controller that receives an input signal from the gimbal platform and provides a stabilization command to the gimbal platform. A lens/detector unit is mounted on the gimbal platform. The lens/detector unit includes a two-color infrared detector having an output signal, a wide-angle lens system having a scene energy input from a pointing direction and a wide-angle-lens output beam focused onto the two-color infrared detector, and a narrow-angle lens system having the scene energy input from the pointing direction and a narrow-angle-lens output beam focused onto the two-color infrared detector. The lens/detector unit also includes a controllable optical switch having as inputs the wide-angle-lens output beam and the narrow angle-lens output beam, and an optical switch output beam, and a beam splitter (preferably a dichroic reflector) that splits the optical switch output beam into a first-color beam that falls onto a first-color region of the two-color infrared detector and a second-color beam that falls onto a second-color region of the two-color infrared detector. A directional countermeasure device (preferably a laser that upsets the seeker of an incoming missile threat) is mounted on the gimbal platform and is aimed in the pointing direction. An electronics unit mounted off the gimbal platform receives the output signal of the two-color infrared detector, analyzes the output signal, and provides command signals to the gimbal-platform servo controller, the two-color infrared detector, and the optical switch. The electronics unit desirably includes tracking logic which, in a searching mode of operation, commands the gimbal-platform servo controller to perform a repeating step-stare tracking mode of operation.
A method for protecting an aircraft uses a self-protection system mounted on a controllable gimbal. The self-protection system comprises a lens/detector unit having a wide-angle lens system, a narrow-angle lens system, a two-color separator that selectably receives scene energy from the wide-angle lens system or the narrow-angle lens system, and a two-color infrared detector that receives the scene energy in two colors from the two-color separator. The self-protection system also includes a directional countermeasure device. The apparatus described above is preferably employed as an integrated unit, for affordability. The method includes the step of searching for a target using the lens/detector unit by the repeated steps of viewing a viewed portion of a scene through the wide-angle lens system using the infrared detector in a staring mode, analyzing the viewed portion of the scene for the presence of a potential target, and, if no potential target is found, stepping the gimbal to a new portion of the scene, and thereafter repeating the steps of viewing, analyzing, and stepping until the potential target is located at a target location in the step of analyzing. Upon finding the potential target at the target location in the step of searching, the method includes the steps of identifying the target by switching the lens/detector unit to the narrow-angle lens system, so that the two-color infrared detector views the potential target at the target location through the narrow-angle lens system, and determining the nature of the potential target as either hostile or not hostile. Upon determining that the potential target is not hostile, the step of searching is repeated. Upon determining that the potential target is hostile, the directional countermeasure device aimed at the hostile target is activated. The aiming of the directional countermeasure device at the target is maintained in the narrow-angle mode as long as targeting is required.
This step-stare approach achieves a substantially greater resolution than possible with a staring system, because the lens/detector is stepped across the field of regard and also because the view may be changed from a wide angle to a narrow angle during the acquisition and identification process. The sensor is used in a wide-angle mode to make the initial acquisition of the potential target, and then switched to the narrow-angle mode for further identification and targeting. The present apparatus operates autonomously and does not require separate guidance by the aircraft itself.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.